The invention relates to a hydraulic valve lifter or valve clearance control element with an operating control system in an internal combustion engine employing a hydraulic operating fluid having a pressure which is dependent on the engine operating state, particularly for use with electro-magnetic valve drives.
Such a hydraulic valve lifter or valve clearance control element is known for example from DE 198 18 893 A1. In this clearance control element, a throttle passage extending from the pressure space to a low pressure return line is provided with a blocking valve, which is open only when the hydraulic fluid pressure exceeds a certain pressure value of the hydraulic fluid being supplied to the pressure space from the outside. The pressure value is so selected that; during normal engine operation, this blocking valve is open. As the hydraulic fluid, generally, the engine oil is used which is subjected to an operating pressure during engine operation. When the engine is shut down and the engine oil is therefore no longer under pressure the blocking valve automatically closes so that no lubricating oil can escape from the pressure space of the valve lifter. Such an oil discharge blockage is required when the engine is shut down in order to prevent the hydraulic valve lifters of those valves, which are open during engine shut-down, to collapse that is loose their normal operating length and become shorter during engine shut-down.
Valve clearance adjustment means of this type are used in connection with camshaft valve drives. Functional problems however may occur especially with electromotive valve drives.
An electromagnetic valve operating mechanism for example is shut down immediately when the engine is turned off. However, the oil pump which is generally driven by the engine crankshaft and which provides the lubricating oil supply is still in operation as long as the crankshaft rotates after the engine is shut off. As a result, the engine oil pressure does not necessarily drop at the same time as the engine is shut down with the result that the blocking valve which prevents engine oil from flowing out of the pressure chamber of the oil lifter is not timely closed. Consequently, while the engine is still rotating after the engine is shut down but the valve operating mechanism and consequently the valves are at rest, engine oil may still flow out of the pressure chamber of the valve lifter if the pressure chamber is pressurized by the relative movable counter parts of the valve lifter. In an electromagnetic valve drive the pressure chamber is normally pressurized by the valve opening and closing springs during engine shutdown as the valve is held in an intermediate base position between the closed and open positions.
In an electromagnetic valve operating mechanism, an improper operation of a valve clearance control element may cause failure of the electromagnetic valve operating mechanism whereby certain valves are not operated. In such a case, the discharge oil from the pressure chamber of the valve clearance control element is maintained because of the oil is at full pressure so that the valve operating length is reduced. In art electromagnetic valve this may result in a change of the start-out position of the electromagnetic valve actuator so that restarting of the actuator becomes impossible without servicing in a repair shop.
It is the object of the present invention to provide a valve operating system with a valve clearance control element by which operation of the valve, particularly an electromagnetically operated valve, is improved.
In an operating system for a hydraulic valve clearance control element of an internal combustion engine, which includes a hydraulic fluid having a pressure that depends on the engine operating state and wherein the hydraulic clearance control element includes a pressure chamber in which a hydraulic fluid volume is maintained for adjusting the length of the hydraulic clearance control element and means for maintaining the fluid volume when, after engine shut down, the pressure of the hydraulic, fluid supplied by an engine fluid pressure source drops below a certain value so as to maintain the hydraulic clearance control element at its operating length during engine shutdown, means are arranged in the hydraulic fluid supply line to the hydraulic valve clearance control element for releasing hydraulic fluid to reduce its pressure below the certain value immediately upon engine, shutdown so as to safely maintain the hydraulic clearance control elements at their operating length.
The invention is based on the general concept to permit closing of a blocking valve in order to retain the oil in the valve clearance control element under certain engine operating conditions when the oil pressure in the expansion chamber of the valve clearance control element is still too high for closing the blocking valve.
A high pressure in the pressure chamber of the valve clearance control element normally prevents a closing of the blocking valve. Means are therefore provided to reduce the oil pressure so as to close the blocking valve in order to retain the oil in the pressure chamber of the valve clearance control element in order to maintain proper clearance during engine shut-down.
The invention will be described below in detail on the basis of the accompanying drawings.